The present invention relates to a semiconductor process, and more particularly, to an improved method of removing photoresist from a semiconductor substrate to improve photoresist rework process and reduce the cycle time.
During the manufacture of semiconductors and semiconductor microcircuits, it is frequently necessary to coat the photoresist materials on the substrate. In a photolithographic process, the photoresist materials are pattern delineation that are evenly and completely removed from all unexposed areas in the case of positive photoresists, so as to permit further lithographic operation. These patterns define different active regions of the circuit, for example, diffusion regions, gate regions, contact regions or interconnection regions and so on, which allow the necessary ion implantation, etching or diffusion process to be performed. The photoresists are used as masking materials to form patterns on to the substrate during etching to protect the selected areas of the surface of the substrate while etchant selectively attacks the unprotected area of the substrate.
The photoresists are developed it is desired to measure the critical dimensions of the pattern as well as to verify their integrity before the pattern is etched. After development, an inspection (sometimes referred to as an after-develop-inspection, ADI) is performed. The purpose is to insure that the steps of the photoresist process up to this point have been performed correctly and to a point within the specified tolerance. Mistakes or unacceptable process variations can be corrected, since the photoresist process has not yet produced any changes to the wafer substrate. Thus, any inadequately processed wafers or wafers, that are misaligned, of unacceptable critical dimension, and embody defective pattern detected by the inspection can have the photoresists stripped or reworked. A misaligned photoresist pattern or a defective photoresist pattern must be removed for reimaging after development and inspection.
There are three types of photoresist stripping methods: organic strippers, oxidizing-type inorganic strippers and dry etching. An alternative method of removing photoresist involves burning the remaining photoresist from the photoresist-covered substrate by oxygen plasma. This process is known as oxygen plasma ashing. Recently, the oxygen plasma ashing method has become the preferred method for removal of photoresist because oxygen plasma can easily burn photoresist to vaporized substances, for example, CO2, CO, H2O and thus remove the photoresist film from the substrate. Also, this dry process is carried out in a vacuum chamber and is less susceptible to particulate or metallic contamination. However, sidewall polymers and other inorganic substances may still be present after the ashing process is complete. Hence, additional steps after oxygen plasma ashing are necessary to remove these residues completely.
One preferred treatment is shown in FIG. 1, the oxygen plasma ashing (step 11) is carefully applied first to partially remove the photoresist film. Subsequently, a wet stripping (step 12) is applied to completely remove organic photoresists, as well as inorganic plasma etching residues in the final step. In the final step, removal of the partially removed photoresists and plasma etching residual is accomplished by exposing the substrate to a wet stripper. For example, sulfuric acid (H2SO4) is used before metal layers, and amine solution is used after metal layers. The main objective in photoresist stripping is to insure that all the photoresist is removed as quickly as possible without attacking any underlying surface materials, especially metal layers.
However, these processes have numerous shortcomings, especially for photoresist reworking. The long stripping time of the processes limits production rate and increases the per-wafer cost of production. In addition, these processes are batch-type, if we have only two wafers need to be reworked, we must spend much time to wait for a batch of reworked wafers for batch-type rework processes. It will increase a cycle time of rework processes, which is about 0.5 to 1.5 days per wafer while the Fab is fully loaded. Thus, the conventional photoresist reworking process has a long cycle time and a large cost.
Thus, there is a need to provide an improved method of reworking photoresist to reduce the cycle time and increase the throughput.
An object of the present invention is to provide an improved process for removing photoresist in less time than prior processes.
Another other object of the present invention is to provide an improved process for reworking misaligned photoresist patterns to reduce cycle time.
The present invention discloses an improved method for reworking photoresist. A semiconductor substrate with an underlying layer is provided for patterning. A positive photoresist is formed on the underlying layer. A photoresist reworking process is performed after an after-development-inspection (ADI) procedure. The photoresist reworking method comprises the following steps. The semiconductor substrate is placed in wet stripper for removing the most portion of the photoresist pattern. Subsequently, the semiconductor substrate is placed in a single-wafer processor and a UV/O3 dry ashing is then performed to remove completely the residual photoresist pattern and expose the underlying layer. A new photoresist layer is deposited on the underlying layer after the photoresist pattern removed completely.